The Collaborative International Dictionary of English v.0.48:

Rudd \Rudd\, n. [See Rud, n.] (Zool.)
   A fresh-water European fish of the Carp family (Leuciscus
   erythrophthalmus). It is about the size and shape of the
   roach, but it has the dorsal fin farther back, a stouter
   body, and red irises. Called also redeye, roud,
   finscale, and shallow. A blue variety is called
   azurine, or blue roach.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rudd
    n 1: European freshwater fish resembling the roach [syn: rudd,
         Scardinius erythrophthalmus]